Newbie needs a shove in the right direction

Discussion in 'The Projects Forum' started by geordielad, May 10, 2013.

  1. geordielad

    Thread Starter New Member

    Apr 27, 2013
    Hi all,
    I did electronics way back in school days and can't remember basics.
    What I'm looking to do is build a circuit using a 555 timer (unless there is something better suited) and a proximity sensor (like a car parking sensor) which will trigger when an object is in the way but have a delay till it switches on. This will then output to a relay.
    The idea is that the sensor won't activate relay till say 5 seconds has passed. The circuit will then keep the relay switched on till the proximity sensor no longer picks anything up.

    I'm just trying to find some pointers and advice on how to build this circuit please. Or if there is any good books or information to brush up on my electronic skills.
    Thankyou for any help in advance
    Regards Neil
  2. edwardholmes91

    Active Member

    Feb 25, 2013
    I would have a looked at this website Electronics Club. There is a wealth of really useful information on this website and if your interested 555 Timers too :)
  3. strantor

    AAC Fanatic!

    Oct 3, 2010
    You could buy an ON-delay relay if you want a solution in a box.

    P.s. you will get better results on the forum if you use a more descriptive thread title. Most of the experts here who could help you design a circuit, well, their time is precious, and they usually don't click on a thread with a generic title like " need help" .
  4. elec_mech

    Senior Member

    Nov 12, 2008
    Welcome to AAC.

    Do you already have a sensor? Most car parking sensors I've seen use ultrasonic sensors to determine distance. If you're just wanting to sense motion, a PIR sensor is good way to go.

    Take a look at this thread to help get you started. It uses a Parallax PIR sensor with a 555.

    Spending a few minutes on a Post-It note, you can use a 555 as a monostable and invert the output. This will mean the inverted output will be high when the 555 is off. Once triggered, the 555 inverted output will be low for five seconds, then go high again. You can then tie the inverted output and the PIR sensor output to an AND gate (or two diodes and a resistor) and connect the output of said gate to a transistor of some sort to drive the relay (or skip the relay and have transistor drive the load directly if is a DC load). Easier to show on a schematic.

    What is it the relay will drive? What is the voltage and current requirements of this load?

    Take a look at the thread and let me know what think and we can more forward.